In recent years, more countries have issued banknotes called polymer banknotes using synthetic paper. Paper used for banknotes is mainly made of vegetable fiber material, but synthetic paper made of synthetic polymer material is used for the purpose of improving durability, water resistance, security, etc.
A polymer banknote is generally made by applying a printing processing to synthetic paper and further applying a coating processing to the synthetic paper. Polymer banknotes made by combination of synthetic paper and vegetable fiber paper, and polymer banknotes having synthetic paper part and vegetable fiber paper part are also being developed. Further, the techniques for polymer banknotes are also used for securities such as gift certificates, checks and bills.
Paper sheets such as the polymer banknotes and the securities might have transparent parts to which a printing processing is not applied. Handling of the paper sheets having the transparent parts is more difficult than handling of the paper sheets having no transparent part. As one example of handling of a paper sheet having a transparent part, handling of a polymer banknote having a transparent part will be described below.
In a banknote handling device for handling banknotes including polymer banknotes, an optical banknote detection sensor, which is a transmissive optical paper sheet detection sensor, might be used to detect banknotes transported along a transport path. Specifically, when the detection state of the optical banknote detection sensor changes from light transmission to light blocking, the leading end of the arrived banknote is detected. When the detection state of the optical banknote detection sensor changes from light blocking to light transmission, the trailing end of the banknote is detected. Light passes though the transparent part of the banknote, and thus the optical banknote detection sensor might erroneously detect the end of the banknote having the transparent part.
Patent Document 1 discloses a banknote handling device including means for detecting a transparent part of a banknote. The means for detecting the transparent part has a plurality of transmissive optical banknote detection sensors arranged in line in a direction orthogonal to the transport direction of the banknote. By comparing the detection results of the plurality of optical banknote detection sensors, it can be determined whether or not the banknote has a transparent part. If it has been determined that the banknote has a transparent part, the device disclosed in Patent Document 1 stops detecting the transparent part thereafter when detecting the banknote by the optical banknote detection sensors. Accordingly, erroneous detection of the end of the banknote is avoided.
Patent Document 2 discloses that the position of the transparent part of the banknote is specified based on an image of the banknote or the magnetic information of the banknote obtained by the recognition unit. The device disclosed in Patent Document 2 regards a portion excluding a transparent part in the entire banknote as a detection area of a sensor. Accordingly, erroneous detection and erroneous determination caused by detection of the transparent part are avoided.
Patent Document 3 discloses a configuration in which the optical axis of a transmissive optical banknote detection sensor is inclined without being orthogonal to the surface of the banknote. If the optical axis is inclined, part of the light is reflected on the surface and the rest passes through the surface in the transparent part of the banknote. The amount of transmitted light at the time of reception decreases by the amount of reflection of the part of the light. This makes it possible to determine that the light has passed through the transparent part of the banknote, and thus erroneous detection can be avoided.
Patent Document 4 discloses a transmissive optical banknote detection sensor having a configuration in which a polarizing plate is arranged on each of a light illumination side and a light reception side so that the polarization directions are orthogonal to each other. With this configuration, when the light is not blocked by the banknote, the light linearly polarized by the polarizing plate on the light illumination side reaches, as it is, the polarizing plate on the light reception side having an angle deviated by 90°. Accordingly, the pass of light is blocked by the polarizing plate on the light reception side. On the other hand, the light linearly polarized by the polarizing plate on the light illumination side is turned to non-polarized diffused light if passing through the transparent part of the banknote. Accordingly, light can be received through the polarizing plate on the light reception side. As such, the optical banknote detection sensor disclosed in Patent Document 4 includes the polarizing plates to detect the presence of the transparent part of the banknote and the position of the transparent part.
Patent Document 5 discloses a transmissive optical banknote detection sensor having a configuration in which based on the that the amount of light having passed through the transparent part of the banknote decreases, if the amount of the received light is less than 100%, it is determined that the light has passed through the transparent part of the banknote, and if the amount of the received light is 100%, it is determined that no banknote is detected between the banknotes. Patent Document 5 also supposes use of an optical paper sheet detection sensor outputting a non-linear output value with respect to an increase or decrease in the amount of received light, and then discloses a technique of a devised detection method in which it is accurately specified whether the received light is light having passed through the transparent part of the banknote or light passing between the banknotes.
Patent Document 6 discloses irradiating light or ultrasonic wave on the banknote and detecting the reflected wave of the light or ultrasonic wave reflected on the surface of the banknote in order to detect the banknote. Accordingly, even if the transparent part is present in the banknote, the avoidance of erroneous detection is attempted.
Patent Document 7 discloses a banknote handling device having a configuration in which the thickness of a banknote is detected. For the detection of the thickness, a pair of rollers facing each other are used. Specifically, the displacement of the rollers when the banknote passes between the pair of rollers to detect the banknote is detected. Accordingly, so-called a double feed failure or chain feed failure in which a plurality of banknotes are transported in an overlapping manner, and a failure in which a part of a banknote is folded are detected.
Similarly, Patent Document 8 also discloses a banknote thickness detection device. The thickness detection device disclosed in Patent Document 8 includes a reference roller extending in a direction orthogonal to the transport direction of the banknote, and a plurality of detection rollers arranged in line in an orthogonal direction and facing the reference roller. Each of the detection rollers is individually displaced depending on the thickness of the banknote passing between the reference roller and the detection roller such that the transport states such as double feed, chain feed, fold, skew of the banknote are detected.
Patent Document 9 discloses a banknote handling device in which a separating mechanism for separating and delivering stacked banknotes one by one includes a banknote thickness detection device to detect a transport state or pass of the banknote.